2.1. Geology of the Cave
The Za Hajovnou cave (49° 40´ N, 16° 55´E) is a former sinkhole located
in the Javoricko Karst in the Moravia region of the Czech Republic
(Lundberg et al., 2014; Musil, 2014) (Fig. 1). The Javoricko Karst was
formed from the dissolution of light-gray-colored massive Devonian
limestone that overlies Precambrian phyllite (Lundberg et al., 2014;
Musil, 2014). The Spranek and Javoricka Rivers flow through the karst.
While Za Hajovnou cave is situated on the northwestern bank of the
Javoricka River on the southern slope of Pani Hora hill (Lundberg et
al., 2014; Žák et al., 2018), both the Spranek and Javoricka watersheds
may have contributed to sediment development in this cave (Fig. 1c).
Za Hajovnou cave is an approximately 500-m-long system (Musil, 2005;
Bábek et al., 2015). Previously, ~200 m of the cave was
explored, and the cave currently consists of two main parallel corridors
with slightly different sedimentological records (Musil, 2014; Musil et
al., 2014) (Fig. 1d). One corridor (local name is “Excavated
Corridor”, which used to be a sinkhole entrance) and the other corridor
(local name is “Birthday Corridor”) have separate entrances, and they
are connected by the Connecting Passage Corridor (Fig. 1d). Sediments
from the Excavated Corridor continue to the Birthday Corridor and
partially fill the Connecting Passage Corridor (Musil et al., 2014)
(Fig. 1d).
The upper sediments in the cave (Fig. 2a and d) were dated by U/Th
dating of flowstones from 118 ± 1 to 267 ± 3 ka, and the sediment spans
the time of the Cromerian Interglacial Complex in northwestern Europe,
which begins with the interglacial period of the marine isotope stage
(MIS 19; 773 ka; Cohen and Gibbard, 2019) and the Matuyama-Brunhes
reversal (Kadlec et al., 2005, 2014; Musil, 2005, 2014; Musil et al.,
2014; Lundberg et al., 2014; Bábek et al., 2015; Žák et al., 2018).
The Matuyama-Brunhes boundary was identified (by Kadlec et al., 2005,
2014) in the upper part of the backwater fine sediments deposited from
suspension (total thickness up to 4.3 m) in the flooded cave. These
sediments underlie mostly nonfluvial deposits that enter the cave
through a steep passage and fill the Connecting Passage Corridor (Kadlec
et al., 2014; Lundberg et al., 2014; Musil et al., 2014).
The sedimentary sections studied by Kadlec et al. (2005, 2014) in the
Excavated Corridor of Za Hajovnou cave were composed of two parts. The
first part, which is 0.8 m thick (Section No. 1, in Fig. 1d) and located
approximately 28 m from the cave entrance, was interpreted by Kadlec et
al. (2014) to contain the Matuyama-Brunhes transition from reversed to
normal polarity. This section corresponds to Bed Nos. 4 and 5 (Fig. 2d)
in Profile 1 (Fig. 1d) of Kadlec et al. (2005). The second part, which
is ~3.3 m thick (Section No. 2 (Profile 2 of Kadlec et
al. (2005)), in Fig. 1d), underlies Section No. 1 and corresponds to the
lower part in Profile 1 of Kadlec et al. (2005) (Fig. 2d). Kadlec et al.
(2014) indicated that this section only contained sediment with reversed
polarity. The interpretation of the paleomagnetic data was difficult
because the magnetization of the sediments was too weak for the
sensitivity of the Agico JR-5A spinner magnetometer. This difficulty was
the motivation for the present research. Here, we collected 44 new
oriented discrete sedimentary samples from the Excavated Corridor near
upper backwater sedimentary Section No. 1 (Fig. 1d and 2).